CNN’s Jake Tapper received information from the White House that contacts on the ground in Ukraine are concerned Russia might invade the country this weekend.

“Sources tell me from the Obama administration is quote very concerned that the Russians are not being truthful when they say their troops currently positioned on Ukraine’s eastern and southern borders are merely there for training exercises,” said Tapper.

The sources stressed they are not definitely sure it will happen, but they are cautious.

On March 16, a referendum in Crimea passed, purportedly showing the province’s intention to leave Ukraine and join the Russian Federation. Western governments, citing a lopsided margin of victory (the vote purportedly went 95% toward secession from Ukraine) and implicit threats of violence from Russia, declared the referendum illegitimate.

The vote alone raised tension between Russia and Ukraine, but to make matters worse, Moscow decided to move over 200,000 troops to Ukraine’s east border. Russian forces engaged in military exercises, which Moscow said were meant to familiarize the soldiers with the land.

Ukraine’s interim president Oleksandr Turchynov’s resolution to build a national guard with 60,000 people was quickly approved in response to Russia President Vladimir Putin’s threat. Many Ukrainians have signed up to offer their services to protect Ukraine.